1. Field of the Invention
The present invention relates to a vehicular air conditioning system.
2. Description of the Related Art
A system is known which utilizes the heat generated from a heating unit such as, for example, an inverter circuit mounted on a vehicle for air conditioning.
For example, in Japanese Patent No. 4285292 (Patent Document 1), in connection with a refrigerating cycle apparatus having a cooling circuit for cooling an in-vehicle heating unit with a cooling medium which is circulated by a cooling medium circulating pump and also having an evaporator which absorbs heat from the cooling medium present in the cooling circuit, there is disclosed a technique related to a method for operating a vehicular cooling system, the vehicular cooling system having in the cooling circuit an inside air conditioning heat exchanger for heat exchange between the cooling medium and air blown off to the interior of a vehicle room. In Patent Document 1, both device cooling and room cooling can be done at a time by using a refrigerating cycle.
In Japanese Patent Laid-Open No. 2008-230594 (Patent Document 2) is disclosed a technique of heating air for air conditioning by both heat generated in a heat pump type cooling apparatus and heat generated with a heater, during room heating. Patent Document 2 discloses that in a vehicle not having such a large heat source as an engine, a sufficient room heating performance can be achieved even when the outside air temperature is extremely low.
In case of performing both heating unit cooling and room cooling at a time using a refrigerating cycle, the prior art involves the problem that the cooling medium temperature cannot always be controlled to a temperature appropriate for both air conditioning load and heating unit, because the prior art is of the construction in which the same cooling medium is supplied to both heating unit and heat exchanger for air conditioning. Therefore, for example when it is necessary to cool the cooling medium to 10° C. or so to effect room cooling, the cooling medium flowing to the heating unit is also cooled to 10° C. or so.
When the heating unit temperature becomes lower than the outside air temperature, heat flows from the outside air to the heating unit, thus giving rise to the necessity that cooling be done extra by an amount corresponding to such input heat in the refrigerating cycle. Thus, there has been the inconvenience that the power consumption in the refrigerating cycle increases.
Moreover, in a certain particular condition there is a fear of dew formation in the interior of the heating unit, thus giving rise to the necessity of taking a measure against dew formation.
According to the construction of Patent Document 2, when making room heating, a cooling medium flowing to a heat exchanger for air conditioning is heated by both a heater and a water-cooled condenser in a refrigerating cycle. Therefore, the condensation temperature in the water-cooled condenser is influenced by the temperature of the cooling medium.
In case of using a heater, the cooling medium temperature rises, so that the condensation temperature in the water-cooled condenser also rises. Once the condensation temperature rises, the power consumption for ensuring the same room heating capacity increases. Thus, in case of using a heater, there has been the problem that the power consumption in the refrigerating cycle also increases, in addition to the power consumption of the heater.
It is an object of the present invention to solve the above-mentioned problems and provide a vehicular air conditioning system with less power consumption.